A number of chemical methods have been conventionally applied to etch, clean or generally, process surfaces of a metallic workpiece for a clear and consistent finish or aesthetically enhanced appearance. For example, workpieces of aluminium and/or aluminium alloys are often surface processed by etching in an aqueous sodium hydroxide solution (NaOH (aq)) (also called “caustic solution” or “caustic soda”) to remove the surface material prior to anodization. This etching step will generally produce a basic surface finish which prepares the workpiece for the subsequent, anodizing steps.
One issue of the caustic surface processing is that the chemical etching involved is a non-selective process and therefore, any markings such as signs, logos or indicia which have been previously provided on the surface of the workpiece, will also be removed along with the surface material of the workpiece and therefore the markings are not retained.